Mobile communication systems are widely developed to provide various types of communication contents, such as voice, data, etc. Such systems may be multiple access systems capable of supporting communication with a plurality of users by sharing available system resources (for example, a bandwidth, transmission power). These multiple access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3 GPP long-term evolution (LTE) systems, and orthogonal frequency division multiple access (OFDMA) systems, for example.
In general, radio multiple access communication systems are simultaneously capable of supporting communications with respect to a plurality of radio terminals. Each of the plurality of radio terminals communicates with one or more base stations through transmissions on a forward or backward link. The forward link (also referred to as a down link or downward link) means a communication link from base stations to terminals, and the backward link (also referred to as an up link or upward link) means a communication link from terminals to base stations. Such communication links can be set using a single input single output (SISO) technique, a multiple input single output (MISO) technique, or a multiple input multiple output (MIMO) technique.
Meanwhile, in the above-described, various types of mobile communication systems, a zone of non radio coverage needs to be covered, or a repeater needs to be configured in a region in which installation costs of base stations are burdened. In general, a superheterodyne type radio frequency (RF) repeater is used. Since the superheterodyne type RF repeater uses an intermediate frequency (IF) surface acoustic wave (SAW) filter having a high Q-value so as to remove selectivity, sensitivity characteristics and video frequency, a basic delay (about 1.5 uS to 2.5 uS) of the SAW filter is reflected on equipment.
That is, the superheterodyne type RF repeater easily removes selectivity, sensitivity, and video frequency and uses the IF of 500 MHz or less so as to use a bandwidth of the general SAW filter. A delay basically occurs in the SAW filter, and a delay (a delay time) of about 1.5 to 2.5 us occurs in the SAW filter that uses a bandwidth of 10 MHz.
As described above, since the existing RF repeater satisfies selectivity and sensitivity characteristics and uses the SAW filter so as to effectively remove video frequency, a delay of another element is added to the basic delay that occurs in the SAW filter such that the existing RF repeater has an equipment delay of at least 2 to 3 uS and due to the equipment delay, there is a limitation in using a high-output RF repeater in the range of a normal cyclic prefix (CP) (about 4.7 uS) of OFDMA.
Also, a conventional IF filter of a repeater for a mobile communication system, i.e., the SAW filter has characteristics of a rapid bandwidth at an IF (70 MHz) but has a disadvantage with a very large group delay of 1.5 to 2.5 uS.